The Kanboard API returns only true/false for many operations without
explaining why they failed. Added OperationFailedError type that
includes operation details and hints about possible causes.
Updated MoveTaskPosition and MoveTaskToProject to use this new error
type, providing users with actionable debugging information instead
of generic "failed to move task" messages.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>